MeSA is the Compound that Triggers Plant Immune Response

Unlike animals, plants lack immune function cells, like T cells, that signal and fight infection. However, scientists have known that there is a mechanism by which the plant alerts its immune system in case of infection. A group of researchers have recently identified the elusive signal molecule: methyl salicylate (MeSA). Methyl salicylate, also known as oil of wintergreen, is a modified form of salicylic acid (SA), the compound from which aspirin is derived.

MeSA was found by the group from Boyce Thompson Institute for Plant Research at Cornell to be responsible for systemic acquired resistance (SAR), wherein a signal will travel from the site of infection to uninfected parts of the plants. SAR is similar to acquired immunity in animals in that it is systemic and long-lasting.

The discovery was made by studying immune response in tobacco expressing the defective enzyme SABP2, responsible for the conversion of MeSa to SA. Researchers showed that SABP2 must be active in the upper, uninfected leaves for systemic acquired resistance to develop properly. By contrast, SABP2 must be inactivated in the infected leaves by binding to SA. This will lead to accumulation of MeSa which can turn on the plant’s defense.

Subscribers to Science can read the full paper at http://www.sciencemag.org/cgi/content/full/318/5847/113 The abstract of the paper is available at http://www.sciencemag.org/cgi/content/abstract/318/5847/113